In honor of !!con, I was trying to think of programming-relevant uses
of double exclamation marks. Other than denoting the end of a particularly funny programming joke
(for example, a mangled homage to a famous paper),
it seemed the best place to look might be in the world of
double factorials. As it turns out, that wasn't as fruitful
as I'd hoped, but I learned something interesting on the way to finding that out, and here it is.

TL;DR

You can learn interesting things about the order of complexity of an algorithm without knowing anything about how it works …